WO2019225269A1 - Printed circuit board substrate and printed circuit board - Google Patents

Abstract

A printed circuit board substrate according to an embodiment of the present disclosure includes: a base film having insulating properties; a sintered layer composed of a plurality of copper particles laminated on at least one surface of the base film; and an electroless copper plating layer laminated on the reverse surface of the sintered layer from the base film and filling the interior of the sintered layer. The reverse surface of the electroless copper plating layer from the sintered layer has a lightness L* of 45.0 to 85.0 inclusive, a chromaticity a* of 5.0 to 25.0 inclusive, and a chromaticity b* of 5.0 to 25.0 inclusive.

Description

Printed wiring board substrate and printed wiring board

The present disclosure relates to a printed wiring board substrate and a printed wiring board. This application claims priority based on Japanese Patent Application No. 2018-101002 filed on May 25, 2018, and incorporates all the content described in the above Japanese application.

2. Description of the Related Art A substrate for a printed wiring board that has a metal layer on the surface of an insulating base film and forms a conductive pattern by etching the metal layer to obtain a flexible printed wiring board is widely used.

In recent years, with the miniaturization and high performance of electronic devices, higher density of printed wiring boards is required. As a printed wiring board substrate that satisfies such a demand for higher density, a printed wiring board substrate with a reduced thickness of the conductive layer is required.

Also, the substrate for a printed wiring board is required to have a high peel strength between the base film and the metal layer so that the metal layer does not peel from the base film when bending stress acts on the flexible printed wiring board.

In response to such a requirement, a first conductive layer is formed by applying and sintering a conductive ink containing copper particles and a metal deactivator on the surface of an insulating base (base film). A substrate for a printed wiring board has been proposed in which an electroless plating layer is formed by electroless plating on a layer, and a second conductive layer is formed on the electroless plating layer by electroplating (Japanese Patent Laid-Open No. 2012). -114152).

The printed wiring board substrate described in the above publication can be reduced in thickness because the metal layer is directly laminated on the surface of the insulating substrate without using an adhesive. Moreover, the base material for printed wiring boards of the said gazette is preventing the fall of the peeling strength of the metal layer by spreading | diffusion of a copper ion by containing a metal deactivator in a sintered compact layer. Moreover, since the base material for printed wiring boards described in the above publication can be manufactured without expensive equipment such as vacuum equipment, it can be provided at a relatively low cost.

JP 2012-114152 A

A printed wiring board substrate according to an aspect of the present disclosure includes an insulating base film, a sintered body layer of a plurality of copper particles laminated on at least one surface of the base film, and the sintered body. An electroless copper plating layer that is laminated on the surface opposite to the base film of the layer and is filled in the sintered body layer, wherein the electroless copper plating layer is sintered. The lightness L * of the surface opposite to the body layer is 45.0 to 85.0, the chromaticity a * is 5.0 to 25.0, and the chromaticity b * is 5.0 to 25.0. .

A printed wiring board according to another aspect of the present disclosure includes an insulating base film, a sintered body layer of a plurality of copper particles laminated on at least one surface of the base film, and the sintered body layer. Electroless copper plating layer laminated on the surface opposite to the base film and filled in the sintered body layer, and electroplating laminated on the surface opposite to the sintered body layer of the electroless copper plating layer A printed wiring board in which the sintered body layer, the electroless copper plating layer, and the electroplating layer are patterned in plan view, and the lightness L * of one surface of the electroless copper plating layer is 45.0 or more and 85.0 or less, chromaticity a * is 5.0 or more and 25.0 or less, and chromaticity b * is 5.0 or more and 25.0 or less.

FIG. 1 is a schematic cross-sectional view illustrating a printed wiring board substrate according to an embodiment of the present disclosure. FIG. 2 is a schematic cross-sectional view illustrating a printed wiring board according to an embodiment of the present disclosure.

[Problems to be solved by the present disclosure]

The substrate for a printed wiring board described in the above publication has been tested by the present inventors. As a result, when it is held in a high temperature and high humidity environment, the peel strength of the metal layer may be lowered. That is, it was confirmed that the printed wiring board substrate described in the above publication may have insufficient weather resistance.

This indication is made | formed based on the above situations, and makes it a subject to provide the base material for printed wiring boards and a printed wiring board which are excellent in a weather resistance.
[Effects of the present disclosure]

The printed wiring board substrate according to one aspect of the present disclosure and the printed wiring board according to another aspect of the present disclosure are excellent in weather resistance.
[Description of Embodiment of Present Disclosure]
A printed wiring board substrate according to an aspect of the present disclosure includes an insulating base film, a sintered body layer of a plurality of copper particles laminated on at least one surface of the base film, and the sintered body. An electroless copper plating layer that is laminated on the surface opposite to the base film of the layer and is filled in the sintered body layer, wherein the electroless copper plating layer is sintered. The lightness L * of the surface opposite to the body layer is 45.0 to 85.0, the chromaticity a * is 5.0 to 25.0, and the chromaticity b * is 5.0 to 25.0. .

The printed wiring board substrate has a lightness L * of 45.0 to 85.0 and a chromaticity a * of 5.0 to 25. The surface of the electroless copper plating layer on the side opposite to the sintered body layer. When the chromaticity b * is 0 or less and the chromaticity b * is 5.0 or more and 25.0 or less, the voids of the sintered body layer are appropriately filled by electroless copper plating, and the base film, the sintered body layer, In addition to improving the peel strength, it is possible to suppress a decrease in peel strength when continuously used in a high temperature and high humidity environment. Further, since the printed wiring board substrate can be produced without special equipment such as vacuum equipment, it can be produced at a relatively low cost despite excellent weather resistance.

In the printed wiring board substrate, the copper particles preferably have an average particle diameter of 1 nm to 500 nm. Thus, when the average particle diameter of the copper particles is within the above range, a dense sintered body layer with few voids can be formed relatively easily, and the peel strength between the base film and the metal layer is further improved. be able to.

In the printed wiring board substrate, the arithmetic average height Sa of the surface on which the sintered body layer of the base film is laminated is preferably 0.01 μm or more and 0.04 μm or less. Thus, when the arithmetic average height Sa of the surface on which the sintered body layer of the base film is laminated is within the above range, the peel strength between the base film and the metal layer can be further improved.

A printed wiring board according to another aspect of the present disclosure includes an insulating base film, a sintered body layer of a plurality of copper particles laminated on at least one surface of the base film, and the sintered body layer. Electroless copper plating layer laminated on the surface opposite to the base film and filled in the sintered body layer, and electroplating laminated on the surface opposite to the sintered body layer of the electroless copper plating layer A printed wiring board in which the sintered body layer, the electroless copper plating layer, and the electroplating layer are patterned in plan view, and the lightness L * of one surface of the electroless copper plating layer is 45.0 or more and 85.0 or less, chromaticity a * is 5.0 or more and 25.0 or less, and chromaticity b * is 5.0 or more and 25.0 or less.

In the printed wiring board, by setting the surface color of the electroless copper plating layer within the above range, the plated copper is appropriately filled in the sintered body layer, and the peel strength between the base film and the sintered body layer In particular, the decrease in peel strength when used for a long time in a high temperature environment is small. Moreover, since the printed wiring board can be manufactured without special equipment such as vacuum equipment, it can be manufactured at a relatively low cost despite excellent weather resistance.

Here, “sintering” is not only a complete sintering state in which particles are firmly bonded, but also a solid bonding in close contact with each other in the previous stage of reaching a complete sintering state. Including such a state. Further, “lightness L *”, “chromaticity a *”, and “chromaticity b *” are values measured according to JIS-Z8781-4 (2013). The “average particle diameter” is an average value of equivalent circle diameters of particles in a cross-sectional scanning electron microscope observation image. The “arithmetic mean height Sa” of the surface on which the sintered body layer of the base film is laminated conforms to ISO-25178 by removing the electroless copper plating layer and the sintered body layer by etching using an acidic solution. It is a value measured as

[Details of Embodiment of the Present Disclosure]
Hereinafter, each embodiment of the printed wiring board substrate according to the present disclosure will be described in detail with reference to the drawings.

[Substrates for printed wiring boards]
A substrate 1 for a printed wiring board in FIG. 1 includes a base film 2 having an insulating property, and a metal layer 3 laminated on one surface of the base film 2.

The metal layer 3 is laminated on one surface of the base film 2, and a sintered body layer 4 formed by sintering a plurality of copper particles, and the opposite side of the sintered body layer 4 from the base film 2. An electroless copper plating layer 5 is provided on the surface. The metal layer 3 may further include an electroplating layer 6 on the surface of the electroless copper plating layer 5 opposite to the sintered body layer 4.

<Base film>
Examples of the material of the base film 2 include flexible resins such as polyimide, liquid crystal polymer, fluororesin, polyethylene terephthalate, and polyethylene naphthalate, paper phenol, paper epoxy, glass composite, glass epoxy, polytetrafluoroethylene, and glass. It is possible to use a rigid material such as a base material, a rigid flexible material in which a hard material and a soft material are combined, and the like. Among these, polyimide is particularly preferable because of its high bonding strength with copper oxide and the like.

Although the thickness of the said base film 2 is set by the printed wiring board using the said base material for printed wiring boards, and is not specifically limited, For example, as a minimum of the average thickness of the said base film 2, 5 micrometers is Preferably, 12 μm is more preferable. On the other hand, the upper limit of the average thickness of the base film 2 is preferably 2 mm, more preferably 1.6 mm. When the average thickness of the said base film 2 is less than the said minimum, there exists a possibility that the intensity | strength of the base film 2 and by extension the said base material for printed wiring boards may become inadequate. On the contrary, when the average thickness of the base film 2 exceeds the upper limit, the printed wiring board substrate may be unnecessarily thick.

The surface of the laminated surface of the sintered body layer 4 in the base film 2 is preferably subjected to a hydrophilic treatment. As the hydrophilic treatment, for example, plasma treatment for irradiating plasma to make the surface hydrophilic, or alkali treatment for making the surface hydrophilic with an alkaline solution can be employed. By subjecting the base film 2 to a hydrophilic treatment, the adhesion with the sintered body layer 4 is improved, and the peel strength of the metal layer 3 can be improved. Further, when the sintered body layer 4 is formed by applying and sintering ink containing copper particles as described later, the surface tension of the ink with respect to the base film 2 is reduced, so that the ink is uniformly applied to the base film 2. It becomes easy to paint.

The lower limit of the arithmetic average height Sa of the surface on which the sintered body layer 4 of the base film 2 is laminated is preferably 0.01 μm. On the other hand, the upper limit of the arithmetic average height Sa of the surface on which the sintered body layer 4 of the base film 2 is laminated is preferably 0.04 μm. When the arithmetic average height Sa of the surface on which the sintered body layer 4 of the base film 2 is laminated is less than the lower limit, the adhesion between the base film 2 and the sintered body layer 4 may be insufficient. is there. Conversely, when the arithmetic average height Sa of the surface on which the sintered body layer 4 of the base film 2 is laminated exceeds the upper limit, voids are easily formed in the vicinity of the interface between the sintered body layer 4 and the base film 2. Therefore, the sintered body layer 4 may be easily peeled off from the base film 2 in a high temperature and high humidity environment. The arithmetic average height Sa can be adjusted by performing surface treatment such as plasma treatment, alkali treatment, and wet blast treatment. Moreover, you may adjust so that the said arithmetic mean height Sa may become the said range at the time of manufacture of the base film 2. FIG.

<Sintered body layer>
The sintered body layer 4 is formed by laminating a plurality of copper particles on one surface of the base film 2. In addition, the sintered body layer 4 has a low porosity by filling the gaps between the copper particles with plated copper when the electroless copper plating layer 5 is formed.

The sintered body layer 4 can be formed, for example, by applying and sintering ink containing the copper particles. Thus, the metal layer 3 can be easily and inexpensively formed on one surface of the base film 2 by using the ink containing copper particles.

The lower limit of the area ratio of the sintered body of copper particles in the cross section of the sintered body layer 4 (not including the area of the plated copper filled in the gaps of the copper particles when the electroless copper plating layer 5 is formed) is 50% Is preferable, and 60% is more preferable. On the other hand, the upper limit of the area ratio of the sintered body of copper particles in the cross section of the sintered body layer 4 is preferably 90%, and more preferably 80%. When the area ratio of the sintered body of the copper particles in the cross section of the sintered body layer 4 is less than the lower limit, there is a possibility that the decrease in peel strength in a high temperature and high humidity environment cannot be sufficiently suppressed. On the contrary, when the area ratio of the sintered body of the copper particles in the cross section of the sintered body layer 4 exceeds the above upper limit, excessive heat may be required at the time of firing, which may damage the base film 2 or the like, The formation of the binder layer 4 is not easy, and the printed wiring board substrate may be unnecessarily expensive.

The lower limit of the average particle diameter of the copper particles in the sintered body layer 4 is preferably 1 nm, and more preferably 30 nm. On the other hand, the upper limit of the average particle diameter of the copper particles is preferably 500 nm, and more preferably 100 nm. When the average particle diameter of the copper particles is less than the lower limit, for example, the dispersibility and stability of the copper particles in the ink are lowered, so that it is not easy to uniformly laminate the surface of the base film 2. There is a fear. On the other hand, when the average particle diameter of the copper particles exceeds the upper limit, the gap between the copper particles becomes large, and it may not be easy to reduce the porosity of the sintered body layer 4.

As a minimum of average thickness of sintered compact layer 4, 50 nm is preferred and 100 nm is more preferred. On the other hand, the upper limit of the average thickness of the sintered body layer 4 is preferably 2 μm, and more preferably 1.5 μm. When the average thickness of the sintered body layer 4 is less than the lower limit, there are many portions where copper particles are not present in a plan view, and the conductivity may be lowered. On the contrary, when the average thickness of the sintered body layer 4 exceeds the upper limit, it may be difficult to sufficiently reduce the porosity of the sintered body layer 4 or the metal layer 3 may be unnecessarily thick. is there.

In the vicinity of the interface between the base film 2 and the sintered body layer 4, copper oxide based on copper of the copper particles or a group derived from the copper oxide (also sometimes referred to as copper oxide) or water based on copper of the copper particles It is preferable that a group derived from copper oxide or its copper hydroxide (sometimes collectively referred to as copper hydroxide or the like) exists. In particular, it is preferable that both the copper oxide and the copper hydroxide exist. These copper oxides and copper hydroxides and the like have a relatively high adhesion to the base film 2 formed from a resin or the like and to the sintered body layer 4 formed from copper. Accordingly, the presence of copper oxide or the like or copper hydroxide in the vicinity of the interface between the base film 2 and the sintered body layer 4 improves the peel strength between the base film 2 and the sintered body layer 4.

The lower limit of the abundance per unit area, such as copper oxide near the interface of the base film 2 and the sintered layer 4, preferably ^{0.1μg / cm 2, 0.15μg / cm} 2 is more preferable. In contrast, the upper limit of the abundance per unit area, such as copper oxide, is preferably 10 [mu] g / cm ^2, more preferably ^{5μg / cm 2, 1μg / cm} 2 is more preferred. When the abundance per unit area of the copper oxide or the like is less than the lower limit, there is a possibility that the effect of improving the peel strength between the base film 2 and the sintered body layer 4 due to the copper oxide is lowered. On the contrary, when the abundance per unit area of the copper oxide or the like exceeds the upper limit, it may be difficult to control the sintering of the copper particles.

The abundance of lower per unit area, such as copper hydroxide near the interface of the base film 2 and the sintered layer 4, preferably ^{0.5μg / cm 2, 1.0μg / cm} 2 is more preferable. On the other hand, the abundance of the upper limit per unit area, such as copper hydroxide, preferably ^{10μg / cm 2, 5μg / cm} 2 is more preferable. When the abundance per unit area of copper hydroxide or the like is less than the lower limit, it may be difficult to control the sintering of copper particles for producing a large amount of copper oxide or the like. On the contrary, when the abundance per unit area of the copper hydroxide or the like exceeds the upper limit, the copper oxide or the like is relatively reduced, so that the peel strength between the sintered body layer 4 and the base film 2 by copper oxide is increased. May not be improved.

The lower limit of the abundance ratio (mass ratio) of copper oxide or the like to copper hydroxide or the like in the vicinity of the interface between the base film 2 and the sintered body layer 4 is preferably 0.1, and more preferably 0.2. On the other hand, the upper limit of the abundance ratio is preferably 5, more preferably 3, and even more preferably 1. When the abundance ratio is less than the lower limit, the amount of copper hydroxide or the like is excessive with respect to copper oxide or the like in the vicinity of the interface, and therefore the peel strength between the base film 2 and the sintered body layer 4 is increased. May not be improved. Conversely, when the abundance ratio exceeds the upper limit, it may be difficult to control the sintering of the copper particles.

<Electroless copper plating layer>
The electroless copper plating layer 5 is formed by performing electroless copper plating on the outer surface of the sintered body layer 4. The electroless copper plating layer 5 is formed so as to impregnate the sintered body layer 4. That is, voids inside the sintered body layer 4 are reduced by filling the gaps between the copper particles forming the sintered body layer 4 with electroless plated copper. Thus, by filling the gaps between the copper particles with the electroless plated copper, the voids between the copper particles are reduced, and the sintered body layer 4 is peeled off from the base film 2 by causing the voids to be a starting point of fracture. Can be suppressed.

The lower limit of the lightness L * of the outer surface of the electroless copper plating layer 5 (the surface opposite to the sintered body layer 4) is preferably 45, more preferably 50, and even more preferably 60. On the other hand, the upper limit of the lightness L * of the outer surface of the electroless copper plating layer 5 is preferably 85, more preferably 80, and even more preferably 70. Further, the lower limit of the chromaticity a * of the outer surface of the electroless copper plating layer 5 is preferably 5, more preferably 8, and even more preferably 10. On the other hand, the upper limit of the chromaticity a * of the outer surface of the electroless copper plating layer 5 is preferably 25, more preferably 20, and even more preferably 18. Further, the lower limit of the chromaticity b * of the outer surface of the electroless copper plating layer 5 is preferably 5, more preferably 8, and even more preferably 10. On the other hand, the upper limit of the chromaticity b * of the outer surface of the electroless copper plating layer 5 is preferably 25, more preferably 20, and still more preferably 18. By setting the color of the outer surface of the electroless copper plating layer 5 within the above range, the sintered body layer 4 is appropriately densified, and the peel strength and weather resistance between the base film 2 and the sintered body layer 4 are improved. be able to.

The lower limit of the average thickness of the electroless copper plating layer 5 formed on the outer surface of the sintered body layer 4 (not including the thickness of the plated copper inside the sintered body layer 4) is preferably 0.2 μm, 0.3 μm is more preferable. On the other hand, the upper limit of the average thickness of the electroless copper plating layer 5 formed on the outer surface of the sintered body layer 4 is preferably 1 μm, and more preferably 0.5 μm. When the average thickness of the electroless copper plating layer 5 formed on the outer surface of the sintered body layer 4 is less than the lower limit, the electroless copper plating layer 5 sufficiently fills the gaps between the copper particles of the sintered body layer 4 Since the porosity cannot be sufficiently reduced, the peel strength between the base film 2 and the metal layer 3 may be insufficient. On the contrary, when the average thickness of the electroless copper plating layer 5 formed on the outer surface of the sintered body layer 4 exceeds the above upper limit, the time required for the electroless copper plating may become long and the manufacturing cost may increase unnecessarily. There is.

<Electroplating layer>
The electroplating layer 6 is laminated by electroplating on the outer surface side of the sintered body layer 4, that is, on the outer surface of the electroless copper plating layer 5. By this electroplating layer 6, the thickness of the metal layer 3 can be adjusted easily and accurately. In addition, the thickness of the metal layer 3 can be increased in a short time by using electroplating.

As the metal used for this electroplating, copper, nickel, silver or the like having good conductivity can be used. Among them, copper or nickel that is inexpensive and excellent in conductivity is particularly preferable.

The thickness of the electroplating layer 6 is set according to the type and thickness of the conductive pattern required for the printed wiring board formed using the printed wiring board substrate 1, and is particularly limited. Not. In general, the lower limit of the average thickness of the electroplating layer 6 is preferably 1 μm and more preferably 2 μm. On the other hand, as an upper limit of the average thickness of the electroplating layer 6, 100 micrometers is preferable and 50 micrometers is more preferable. If the average thickness of the electroplating layer 6 is less than the lower limit, the metal layer 3 may be easily damaged. Conversely, when the average thickness of the electroplating layer 6 exceeds the above upper limit, the printed wiring board substrate 1 may be unnecessarily thick, or the printed wiring board substrate 1 has insufficient flexibility. There is a risk of becoming.

[Method of manufacturing substrate for printed wiring board]
The printed wiring board substrate manufacturing method includes a step of forming copper particles, a step of preparing ink using the copper particles obtained in the copper particle forming step, and an ink obtained in the ink preparation step. The step of coating on one surface of the insulating base film 2, the step of sintering the ink coating film formed in this coating step, and the sintered body layer 4 formed in this sintering step The lightness L * of the surface is 45.0 to 85.0, the chromaticity a * is 5.0 to 25.0, and the chromaticity b * is 5.0 to 25.0. A step of performing electrolytic copper plating and a step of performing electroplating on the outer surface side of the sintered body layer 4 (the outer surface of the electroless copper plating layer).

<Copper particle formation process>
Examples of the method for forming copper particles in the copper particle forming step include a high temperature treatment method, a liquid phase reduction method, a gas phase method, and the like. Among them, the copper particles are reduced by reducing copper ions with a reducing agent in an aqueous solution. A liquid phase reduction method for precipitation is preferably used.

The liquid phase reduction method is, for example, a reduction process in which copper ions are reduced by a reducing agent for a certain period of time in a solution in which a water-soluble copper compound that forms copper particles in water and a dispersant are dissolved. Is provided.

Examples of water-soluble copper compounds that are the source of copper ions include copper (II) nitrate (Cu (NO ₃ ) ₂ ), copper (II) sulfate pentahydrate (CuSO ₄ .5H ₂ O), and the like. Can do.

As the reducing agent for forming copper particles by the liquid phase reduction method, various reducing agents capable of reducing and precipitating copper ions in a liquid phase (aqueous solution) reaction system can be used. Examples of the reducing agent include sodium borohydride, sodium hypophosphite, hydrazine, transition metal ions such as trivalent titanium ions and divalent cobalt ions, reducing sugars such as ascorbic acid, glucose and fructose, ethylene Examples thereof include polyhydric alcohols such as glycol and glycerin.

Among these, the titanium redox method is a method in which copper ions are reduced by the redox action when trivalent titanium ions are oxidized to tetravalent and copper particles are precipitated. Copper particles obtained by the titanium redox method have a small and uniform particle diameter, and have a shape close to a sphere. For this reason, a dense layer of copper particles can be formed, and voids in the sintered body layer 4 can be easily reduced.

To adjust the particle size of the copper particles, the types and blending ratios of the copper compound, dispersant, and reducing agent are adjusted. Furthermore, what is necessary is just to adjust stirring speed, temperature, time, pH, etc. in the reduction | restoration process which carries out a reduction reaction of a copper compound.

Particularly, the lower limit of the temperature in the reduction step is preferably 0 ° C, more preferably 15 ° C. On the other hand, as an upper limit of the temperature in a reduction process, 100 degreeC is preferable, 60 degreeC is more preferable, and 50 degreeC is further more preferable. If the temperature in the reduction step is less than the lower limit, the reduction reaction efficiency may be insufficient. On the contrary, when the temperature in the reduction process exceeds the above upper limit, the growth rate of the copper particles is high, and the adjustment of the particle size may not be easy.

The pH of the reaction system in the reduction step is preferably 7 or more and 13 or less in order to obtain copper particles having a minute particle size as in this embodiment. At this time, the pH of the reaction system can be adjusted to the above range by using a pH adjuster. As this pH adjuster, common acids or alkalis such as hydrochloric acid, sulfuric acid, sodium hydroxide, sodium carbonate are used. In particular, nitric acid or ammonia containing no impurity elements is used to prevent deterioration of peripheral members. Is preferred. Examples of the impurities include alkali metals, alkaline earth metals, halogen elements such as chlorine, sulfur, phosphorus, and boron.

<Ink preparation process>
In the ink preparation step, an ink containing copper particles that form the sintered body layer 4 is prepared.
As the ink containing copper particles, an ink containing a dispersion medium of copper particles and a dispersant for uniformly dispersing the copper particles in the dispersion medium is preferably used. By using the ink in which the copper particles are uniformly dispersed in this way, the copper particles can be uniformly attached to the surface of the base film 2, and the uniform sintered body layer 4 is formed on the surface of the base film 2. Can do.

The dispersant contained in the ink is not particularly limited, but a polymer dispersant having a molecular weight of 2,000 to 300,000 is preferably used. Thus, by using a polymer dispersant having a molecular weight in the above range, the copper particles can be well dispersed in the dispersion medium, and the film quality of the obtained sintered body layer 4 is dense and free of defects. Can be. When the molecular weight of the dispersant is less than the lower limit, there is a possibility that the effect of preventing the aggregation of copper particles and maintaining the dispersion may not be obtained sufficiently. As a result, the sintered body layer laminated on the base film 2 May not be able to be made dense with few defects. On the contrary, when the molecular weight of the dispersant exceeds the upper limit, the volume of the dispersant is too large, and in the sintering step performed after ink coating, there is a risk of inhibiting the sintering of the copper particles and causing voids. is there. Moreover, when the volume of a dispersing agent is too large, there exists a possibility that the compactness of the film quality of the sintered compact layer 4 may fall, or the decomposition residue of a dispersing agent may reduce electroconductivity.

The above dispersant is preferably free of sulfur, phosphorus, boron, halogen and alkali from the viewpoint of preventing deterioration of parts. Preferred dispersants are those having a molecular weight in the above range, amine-based polymer dispersants such as polyethyleneimine and polyvinylpyrrolidone, and hydrocarbon-based hydrocarbons having a carboxylic acid group in the molecule such as polyacrylic acid and carboxymethylcellulose. Polar groups such as polymer dispersants, poval (polyvinyl alcohol), styrene-maleic acid copolymers, olefin-maleic acid copolymers, or copolymers having a polyethyleneimine moiety and a polyethylene oxide moiety in one molecule The polymer dispersing agent which has can be mentioned.

The above-mentioned dispersant can be added to the reaction system in the form of a solution dissolved in water or a water-soluble organic solvent. As a content rate of a dispersing agent, 1 to 60 mass parts is preferable per 100 mass parts of copper particles. The dispersing agent surrounds the copper particles to prevent aggregation and to disperse the copper particles satisfactorily. However, when the content of the dispersing agent is less than the lower limit, the aggregation preventing effect may be insufficient. On the contrary, when the content ratio of the dispersant exceeds the above upper limit, in the sintering step after the ink application, excessive dispersant may inhibit the sintering of the copper particles, and voids may be generated. The decomposition residue of the polymer dispersant may remain in the sintered body layer as an impurity, thereby reducing the conductivity.

The content ratio of water serving as a dispersion medium in the ink is preferably 20 parts by mass or more and 1900 parts by mass or less per 100 parts by mass of the copper particles. The water of the dispersion medium sufficiently swells the dispersant and disperses the copper particles surrounded by the dispersant well, but when the water content is less than the lower limit, the swelling effect of this dispersant by water May become insufficient. On the contrary, when the content ratio of the water exceeds the upper limit, the copper particle ratio in the ink is decreased, and there is a possibility that a good sintered body layer having the necessary thickness and density cannot be formed on the surface of the base film 2. is there.

A variety of water-soluble organic solvents can be used as the organic solvent blended into the ink as necessary. Specific examples thereof include alcohols such as methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, isobutyl alcohol, sec-butyl alcohol and tert-butyl alcohol, ketones such as acetone and methyl ethyl ketone, Examples thereof include polyhydric alcohols such as ethylene glycol and glycerin and other esters, and glycol ethers such as ethylene glycol monoethyl ether and diethylene glycol monobutyl ether.

The content ratio of the water-soluble organic solvent is preferably 30 parts by mass or more and 900 parts by mass or less per 100 parts by mass of the copper particles. When the content ratio of the water-soluble organic solvent is less than the lower limit, the effects of adjusting the viscosity and vapor pressure of the dispersion with the organic solvent may not be sufficiently obtained. On the other hand, when the content ratio of the water-soluble organic solvent exceeds the upper limit, the swelling effect of the dispersant by water becomes insufficient, and the copper particles may be aggregated in the ink.

In addition, when producing copper particles by the liquid phase reduction method, the copper particles precipitated in the reaction system of the liquid phase (aqueous solution) are once powdered through steps such as filtration, washing, drying, and crushing. An ink can be prepared using the above. In this case, an ink containing copper particles may be prepared by blending powdered copper particles, water as a dispersion medium, a dispersant, and, if necessary, a water-soluble organic solvent in a predetermined ratio. it can. However, it is preferable to prepare an ink using a liquid phase (aqueous solution) in which copper particles are precipitated as a starting material. Specifically, the liquid phase (aqueous solution) containing the precipitated copper particles is subjected to treatment such as ultrafiltration, centrifugation, washing with water, and electrodialysis to remove impurities, and if necessary, concentrated to remove water. . Or conversely, after adding water and adjusting the density | concentration of a copper particle, the ink containing a copper particle is prepared by mix | blending a water-soluble organic solvent in a predetermined | prescribed ratio further as needed. In this method, generation of coarse and irregular particles due to aggregation of copper particles during drying can be prevented, and a dense and uniform sintered body layer 4 can be easily formed.

<Coating process>
In the coating step, the ink is applied to one surface of the base film 2. As a method for coating the ink, conventionally known coating methods such as spin coating, spray coating, bar coating, die coating, slit coating, roll coating, and dip coating can be used. Further, for example, ink may be applied to only a part of one surface of the base film 2 by screen printing, a dispenser, or the like.

<Sintering process>
In the sintering step, the ink coating applied to one surface of the base film 2 is preferably dried and then sintered by heat treatment. As a result, the solvent and dispersant of the ink are evaporated or thermally decomposed, and the remaining copper particles are sintered and the sintered body layer 4 fixed to one surface of the base film 2 is obtained.

In particular, the color of the surface of the electroless copper plating layer 5 can be adjusted by performing a drying process and adjusting the amount of moisture remaining on the surface of the coating film, followed by heat treatment.

Further, in the vicinity of the interface of the sintered body layer 4 with the base film 2, the copper particles are oxidized during the sintering, thereby suppressing generation of copper hydroxide based on copper of the copper particles or a group derived from the copper hydroxide. Meanwhile, copper oxide based on copper of the copper particles or a group derived from the copper oxide is generated. Specifically, for example, when copper is used as the copper particles, copper oxide and copper hydroxide are generated in the vicinity of the interface between the sintered body layer 4 and the base film 2. Since the copper oxide produced in the vicinity of the interface of the sintered body layer 4 is strongly bonded to the polyimide constituting the base film 2, the peel strength between the base film 2 and the sintered body layer 4 is increased.

The sintering is preferably performed in an atmosphere containing a certain amount of oxygen. The lower limit of the oxygen concentration in the atmosphere during sintering is preferably 1 volume ppm, and more preferably 10 volume ppm.
On the other hand, the upper limit of the oxygen concentration is preferably 10,000 volume ppm, more preferably 1,000 volume ppm. When the oxygen concentration is less than the lower limit, the amount of copper oxide generated in the vicinity of the interface of the sintered body layer 4 is reduced, and the adhesion between the base film 2 and the sintered body layer 4 may not be sufficiently improved. . On the contrary, when the oxygen concentration exceeds the upper limit, the copper particles are excessively oxidized and the conductivity of the sintered body layer 4 may be lowered.

The lower limit of the sintering temperature is preferably 150 ° C and more preferably 200 ° C. On the other hand, the upper limit of the sintering temperature is preferably 500 ° C, more preferably 400 ° C. When the sintering temperature is less than the lower limit, the amount of copper oxide generated in the vicinity of the interface of the sintered body layer 4 is reduced, and the adhesion between the base film 2 and the sintered body layer 4 cannot be sufficiently improved. There is a fear. Conversely, when the sintering temperature exceeds the upper limit, the base film 2 may be deformed when the base film 2 is an organic resin such as polyimide.

<Electroless copper plating process>
In the electroless copper plating step, electroless copper plating is performed on the surface opposite to the base film 2 of the sintered body layer 4 laminated on one surface of the base film 2 in the sintering step. A plating layer 5 is formed.

The electroless copper plating is preferably performed together with processes such as a cleaner process, a water washing process, an acid treatment process, a water washing process, a pre-dip process, an activator process, a water washing process, a reduction process, a water washing process, and a drying process.

Further, it is preferable to further perform heat treatment after forming the electroless copper plating layer 5 by electroless copper plating. When heat treatment is performed after the formation of the electroless copper plating layer 5, copper oxide or the like in the vicinity of the interface of the sintered body layer 4 with the base film 2 further increases, and the adhesion between the base film 2 and the sintered body layer 4. Becomes even larger. The heat treatment temperature and oxygen concentration after electroless copper plating can be the same as the sintering temperature and oxygen concentration in the sintering step.

<Electroplating process>
In the electroplating step, the electroplating layer 6 is laminated on the outer surface of the electroless copper plating layer 5 by electroplating. In this electroplating step, the entire thickness of the metal layer 3 is increased to a desired thickness.

In this electroplating, for example, a conventionally known electroplating bath corresponding to a metal to be plated such as copper, nickel, silver or the like is used, and appropriate conditions are selected. Can be made to form.

〔advantage〕
The printed wiring board substrate 1 is sintered with the base film 2 even in a high-temperature and high-humidity environment by setting the color of the surface of the electroless copper plating layer opposite to the sintered body layer within the above-mentioned range. The decrease in peel strength with the body layer 4 and the metal layer 3 is small, and the weather resistance is excellent.

Moreover, since the printed wiring board substrate 1 can be manufactured without special equipment such as vacuum equipment, it is manufactured at a relatively low cost despite the high peel strength between the base fill 2 and the metal layer 3. can do.

[Printed wiring board]
The printed wiring board is formed by using the subtractive method or the semi-additive method using the printed wiring board substrate 1 of FIG. More specifically, the printed wiring board is manufactured by forming a conductive pattern by a subtractive method or a semi-additive method using the metal layer 3 of the printed wiring board substrate 1.

In the subtractive method, a photosensitive resist is formed on the surface of the metal layer 3 of the printed wiring board substrate 1 in FIG. 1, and patterning corresponding to the conductive pattern is performed on the resist by exposure, development, or the like. . Subsequently, the metal layer 3 other than the conductive pattern is removed by etching using the patterned resist as a mask. Finally, by removing the remaining resist, the printed wiring board having a conductive pattern formed from the remaining portion of the metal layer 3 of the printed wiring board substrate 1 is obtained.

In the semi-additive method, a photosensitive resist is formed on the surface of the metal layer 3 of the printed wiring board substrate 1 shown in FIG. 1, and openings corresponding to the conductive pattern are patterned on the resist by exposure, development, and the like. To do. Subsequently, by performing plating using the patterned resist as a mask, a conductor layer is selectively laminated using the metal layer 3 exposed in the opening of the mask as a seed layer. Thereafter, the resist layer is peeled off, and then the surface of the conductor layer and the metal layer 3 on which the conductor layer is not formed are removed by etching, whereby the metal layer of the printed wiring board substrate 1 as shown in FIG. The printed wiring board having a conductive pattern formed by laminating a further conductor layer 7 on the remaining part of 3 is obtained.

〔advantage〕
Since the printed wiring board is manufactured using the printed wiring board substrate 1, the decrease in the adhesion between the base film 2 and the sintered body layer 4 is small even in a high-temperature and high-humidity environment, and the weather resistance is excellent. Therefore, the conductive pattern is difficult to peel off.

Moreover, since the printed wiring board is formed by a general subtractive method or semi-additive method using the inexpensive substrate 1 for printed wiring board, it can be manufactured at low cost.

[Other Embodiments]
The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is not limited to the configuration of the embodiment described above, but is defined by the scope of the claims, and is intended to include all modifications within the meaning and scope equivalent to the scope of the claims. The

The printed wiring board substrate may have metal layers formed on both sides of the base film.

The substrate for a printed wiring board may not have an electroplating layer particularly when used for producing a printed wiring board by a semi-additive method.

Further, the sintered body layer of the printed wiring board substrate may be formed by laminating and sintering copper particles on the surface of the base film by other means without using ink.

Hereinafter, the present invention will be described in detail based on examples, but the present invention is not construed as being limited based on the description of the examples.

<Prototype substrate for printed wiring board>
In order to verify the effect of the present disclosure, the prototype No. with different manufacturing conditions was used. Four types of printed wiring board substrates 1 to 4 were produced. Prototype No. of these printed wiring board substrates 1-No. For 4, the color of the surface of the electroless copper plating layer and the peel strength of the metal layer before and after the weather resistance test were measured.

(Prototype No. 1)
First, copper particles having an average particle diameter of 75 nm were used as copper particles, and this was dispersed in water as a solvent to prepare an ink having a copper concentration of 26% by mass. Next, a polyimide film having an average thickness of 12 μm (“Apical NPI” manufactured by Kaneka Corporation) is used as an insulating base film, and the ink is applied to one surface of the polyimide film and dried in the air. Further, moisture on the surface was removed by blowing compressed air to form a dry coating film having an average thickness of 0.15 μm.
The surface roughness of the formed ink layer was 0.032 μm. Subsequently, the polyimide film on which the dried coating film was formed was sintered at 350 ° C. for 2 hours in a nitrogen atmosphere having an oxygen concentration of 10 ppm by volume to form a sintered body layer. And the electroless plating of copper was performed on the surface opposite to the base film of the sintered body layer to form an electroless copper plating layer having an average thickness from the outer surface of the sintered body layer of 0.25 μm. In addition, heat treatment was performed at 350 ° C. for 2 hours in a nitrogen atmosphere having an oxygen concentration of 150 ppm by volume, and the prototype No. of a printed wiring board substrate was obtained. 1 was obtained. This prototype No. The surface color of the electroless copper plating layer 1 has a lightness L * of 70.4 to 64.5, a chromaticity a * of 13.6 to 14.7, and a chromaticity b * of 13.1 to 14.9. Met. Prototype No. For No. 1, the peel strength before the weather resistance test was 7.1 to 9.4 N / cm, whereas the peel strength after the weather resistance test was 5.3 to 5.7 N / cm.

(Prototype No. 2)
First, copper particles having an average particle diameter of 75 nm were used as copper particles, and this was dispersed in water as a solvent to prepare an ink having a copper concentration of 26% by mass. Next, a polyimide film having an average thickness of 12 μm (“Apical NPI” manufactured by Kaneka Corporation) is used as an insulating base film, and the ink is applied to one surface of the polyimide film and dried in the air. Furthermore, moisture on the surface was removed by blowing compressed air to form a dry coating film having an average thickness of 0.18 μm.
The surface roughness of the formed ink layer was 0.092 μm. Subsequently, the polyimide film on which the dried coating film was formed was sintered at 350 ° C. for 2 hours in a nitrogen atmosphere having an oxygen concentration of 10 ppm by volume to form a sintered body layer. And the electroless plating of copper was performed on the surface opposite to the base film of the sintered body layer to form an electroless copper plating layer having an average thickness from the outer surface of the sintered body layer of 0.25 μm. In addition, heat treatment was performed at 350 ° C. for 2 hours in a nitrogen atmosphere having an oxygen concentration of 150 ppm by volume, and the prototype No. of a printed wiring board substrate was obtained. 1 was obtained. This prototype No. The surface color of the electroless copper plating layer 2 was as follows: lightness L * was 54 to 60.1, chromaticity a * was 12.2 to 13.5, and chromaticity b * was 9.9 to 11.8. It was. Prototype No. For No. 2, the peel strength before the weather resistance test was 7.4 to 8.7 N / cm, whereas the peel strength after the weather resistance test was 5.0 to 5.5 N / cm.

(Prototype No. 3)
First, copper particles having an average particle diameter of 75 nm were used as copper particles, and this was dispersed in water as a solvent to prepare an ink having a copper concentration of 26% by mass. Next, a polyimide film having an average thickness of 12 μm (“Apical NPI” manufactured by Kaneka Corporation) is used as the insulating base film, and the ink is applied to one surface of the polyimide film and dried in the air. A dry coating film having an average thickness of 0.15 μm was formed. The surface roughness of the formed ink layer was 0.032 μm. Subsequently, the polyimide film on which the dried coating film was formed was sintered at 350 ° C. for 2 hours in a nitrogen atmosphere having an oxygen concentration of 10 ppm by volume to form a sintered body layer. And the electroless plating of copper was performed on the surface opposite to the base film of the sintered body layer to form an electroless copper plating layer having an average thickness from the outer surface of the sintered body layer of 0.25 μm. In addition, heat treatment was performed at 350 ° C. for 2 hours in a nitrogen atmosphere having an oxygen concentration of 150 ppm by volume, and the prototype No. of a printed wiring board substrate was obtained. 3 was obtained. This prototype No. The surface color of the electroless copper plating layer 1 has a lightness L * of 37.6 to 38.4, a chromaticity a * of 9.9 to 11.6, and a chromaticity b * of 5.9 to 10.3. Met. Prototype No. For No. 3, the peel strength before the weather resistance test was 7.4 to 8.7 N / cm, whereas the peel strength after the weather resistance test was 3.8 to 4.8 N / cm.

(Prototype No. 4)
First, copper particles having an average particle diameter of 75 nm were used as copper particles, and this was dispersed in water as a solvent to prepare an ink having a copper concentration of 26% by mass. Next, a polyimide film having an average thickness of 12 μm (“Apical NPI” manufactured by Kaneka Corporation) is used as the insulating base film, and the ink is applied to one surface of the polyimide film and dried in the air. A dry coating film having an average thickness of 0.18 μm was formed. The surface roughness of the formed ink layer was 0.092 μm. Subsequently, the polyimide film on which the dried coating film was formed was sintered at 350 ° C. for 2 hours in a nitrogen atmosphere having an oxygen concentration of 10 ppm by volume to form a sintered body layer. And the electroless plating of copper was performed on the surface opposite to the base film of the sintered body layer to form an electroless copper plating layer having an average thickness from the outer surface of the sintered body layer of 0.25 μm. In addition, heat treatment was performed at 350 ° C. for 2 hours in a nitrogen atmosphere having an oxygen concentration of 150 ppm by volume, and the prototype No. of a printed wiring board substrate was obtained. 4 was obtained. This prototype No. The surface color of the electroless copper plating layer 1 has a lightness L * of 33.8 to 35.4, a chromaticity a * of 5.1 to 8.5, and a chromaticity b * of -3.9 to -5. .1. Prototype No. For No. 4, the peel strength before the weather resistance test was 7.4 to 8.7 N / cm, whereas the peel strength after the weather resistance test was 3.0 to 4.6 N / cm.

<Color of electroless copper plating layer>
Prototype No. of substrate for printed wiring board 1-No. The color of No. 4 was measured at a plurality of locations as color coordinates in accordance with JIS-Z8781-4 (2013). For the measurement of color, “COLOR CR20” manufactured by Konica Minolta Co., Ltd. was used.

<Weather resistance test>
The weather resistance test was conducted in accordance with JIS-D0205 (1987) under the environment of a temperature of 63 ± 3 ° C. and a humidity of 50 ± 5%. 1-No. 4 was irradiated with a sunshine carbon arc lamp (255 W / m ² ) for 1000 hours.

<Peel strength>
Prototype No. of substrate for printed wiring board before and after weather resistance test 1-No. The peel strength of No. 4 was measured by a method in which a plurality of test pieces were cut out and performed according to JIS-C6471 (1995), and the metal layer was peeled off from the base film in the direction of 180 °.

Prototype No. of substrate for printed wiring board 1-No. The peel strength before and after the weather resistance test 4 and the color of the electroless copper plating layer are summarized in Table 1 below.

Thus, the lightness L * of the surface opposite to the sintered body layer of the electroless copper plating layer is 45.0 to 85.0, the chromaticity a * is 5.0 to 25.0, and the chromaticity b Prototype No. with * between 5.0 and 25.0 1 and no. In No. 2, the decrease in peel strength by the weather resistance test was relatively small. On the other hand, the lightness L * of the surface opposite to the sintered body layer of the electroless copper plating layer is less than 45.0. No. 3 and prototype No. in which the chromaticity b * of the surface opposite to the sintered body layer of the electroless copper plating layer is less than 5.0. No. 4 had a relatively large decrease in peel strength due to the weather resistance test.

DESCRIPTION OF SYMBOLS 1 Base material for printed wiring boards 2 Base film 3 Metal layer 4 Sintered body layer 5 Electroless copper plating layer 6 Electroplating layer 7 Conductor layer

Claims (4)

An insulating base film;
A sintered body layer of a plurality of copper particles laminated on at least one surface of the base film;
A substrate for a printed wiring board comprising: an electroless copper plating layer laminated on a surface opposite to the base film of the sintered body layer and filled in the sintered body layer;
The lightness L * of the surface opposite to the sintered body layer of the electroless copper plating layer is 45.0 or more and 85.0 or less, the chromaticity a * is 5.0 or more and 25.0 or less, and the chromaticity b * is 5 A printed wiring board substrate having a thickness of from 0 to 25.0. The printed wiring board substrate according to claim 1, wherein the copper particles have an average particle diameter of 1 nm to 500 nm. 3. The printed wiring board substrate according to claim 1, wherein the arithmetic average height Sa of the surface on which the sintered body layer of the base film is laminated is 0.01 μm or more and 0.04 μm or less. An insulating base film;
A sintered body layer of a plurality of copper particles laminated on at least one surface of the base film;
An electroless copper plating layer laminated on the surface opposite to the base film of the sintered body layer and filled in the sintered body layer;
An electroplating layer laminated on the surface opposite to the sintered body layer of the electroless copper plating layer,
The printed wiring board in which the sintered body layer, electroless copper plating layer and electroplating layer are patterned in plan view,
The lightness L * of one surface of the electroless copper plating layer is 45.0 or more and 85.0 or less, the chromaticity a * is 5.0 or more and 25.0 or less, and the chromaticity b * is 5.0 or more and 25.0. Printed wiring board which is the following.

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